Waves/Transcript
Text reads: The Mysteries of Life with Tim and Moby A robot, Moby, is playing with a Slinky toy on a staircase. The toy moves down the steps, away from Moby. Moby weeps. MOBY: Beep. Beep. Beep. A boy, Tim, reads from a typed letter. TIM: Dear Tim and Moby, Are light waves, sound waves, and ocean waves all the same thing? From, Danny. Well, all waves do the same basic thing: transfer energy from one place to another. But physicists divide waves into two basic kinds: mechanical and electromagnetic. Images show a mechanical wave and an electromagnetic wave. TIM: Ocean waves, seismic waves, sound waves, and Slinky waves are all mechanical waves, because they need a medium to move through. Images show the four kinds of mechanical waves as Tim names them. MOBY: Beep. TIM: Well, a medium is any kind of matter that's disturbed by energy. That energy disperses through the medium in the form of waves, which are basically chains of vibrating molecules. An animation shows a rock dropping into a pond. TIM: Water waves move energy through the medium of water molecules. Animations show ripples and moving water molecules. TIM: Sound waves can transfer energy through a medium of air, liquid, or solid molecules. An animation shows a tuning fork being struck and waves going into the air. TIM: Seismic waves travel through the ground, usually after an earthquake. An animation shows a neighborhood shaking. TIM: And Slinky waves move through the medium of individual loops. An animation shows a Slinky going down a staircase. TIM: Slinkies are really useful for visualizing how mechanical waves work. You can think of each ring as an individual molecule. An image shows slinky rings split into individual molecules in a horizontal row. TIM: When you shake one end of the toy, you can see how the kinetic energy moves from one Slinky molecule to the next. Mechanical waves may appear to move matter forward with them, but that's not the case. Just like with a Slinky's rings, a molecule disturbed by a wave will return to its original resting position after it's passed the energy on to its neighbors. The slinky molecules move in a wave formation to illustrate Tim's explanation. MOBY: Beep. TIM: Electromagnetic waves, like light and radio waves, don't need a medium to move through; they can travel through completely empty space. An image shows the spectrum of electromagnetic waves, from gamma waves to radio waves, including the range of visible light. TIM: That's why light waves from the Sun and stars are able to reach Earth. An animation shows the Sun’s rays shining on the earth. TIM: And why radio waves let us communicate with spacecraft. An image shows a NASA control room. MOBY: Beep. TIM: Well, mechanical and electromagnetic waves are different, but they can be measured in many of the same ways. This particular wave is called a transverse wave. It carries energy along the spring by making it move at right angles to the direction of the energy flow. Tim holds one end of a long spring and moves it up and down, creating waves. TIM: Ocean waves and most electromagnetic waves move in a transverse pattern. The crest is the highest point of a transverse wave, and the trough is the lowest point. That distance between the midpoint of the wave and the crest is the amplitude. That's also a measure of how much energy the wave is carrying. More energy means a greater amplitude. The distance a wave travels in one wave cycle is one wavelength. That's measured by finding the distance between two crests or two troughs. An image shows a transverse wave with its parts labeled. MOBY: Beep. TIM: Waves can be measured by their frequency, too. The frequency is the number of waves that pass a given point in one second. It's measured in hertz, or waves per second. An animation illustrates waves of different frequencies passing a specific point. TIM: And frequency is related to wavelength. A wave with a short wavelength will have a high frequency, while a wave with a long wavelength will have a low frequency. Images show different wavelengths. MOBY: Beep. Moby holds a boom box to his ear. He turns it on. There is static and random noise. TIM: Right. Sound travels in compressional waves. Unlike transverse waves, compressional waves displace matter back and forth in the same direction as the energy of the wave. Tim and Moby each hold one end of a long spring. Tim gives his end a push and a compressional wave moves forward through the spring, toward Moby. TIM: Vibrations created by anything from your vocal cords, to a drum head, to breaking glass will push air molecules together, forming a series of compressions that travel through the air. An animation shows compressional waves making contact with a human ear. TIM: Those compressing molecules hit your eardrum, making it vibrate and sending sound signals to your brain. Tim holds one end of a long spring. TIM: Like I said, mechanical waves need something to travel through. Moby drifts through space wearing a spacesuit. TIM: That's why you won't hear sounds if you find yourself in outer space. Unless, of course, if you bring your own air. MOBY: Beep. TIM: Well, that's about enough on waves for now. Say goodnight, Moby. MOBY: Beep. Moby is still holding the other end of the spring that Tim has been holding. He releases it in order to wave goodbye. The spring snaps and hits Tim. TIM: Ow! Category:BrainPOP Transcripts Category:BrainPOP Science Transcripts